Prostate cancer (PCa) is the most frequently diagnosed malignancy and the second leading cause of cancer deaths in men in the United States. Epidemiological studies suggest that regular use of non-steroidal anti-inflammatory drugs (NSAIDs), including aspirin, might be as protective against prostate cancer as it is against colon cancer. Chemoprevention has the potential to be an important component of prostate cancer control. Along these lines unraveling the cellular and molecular events mediated by known chemopreventive agents such as celecoxib is an urgent and attractive challenge to enhance chemopreventive efficacy but minimize dose-dependent toxicity. More importantly, identifying the modes of action of a single agent that modulates more than one molecular target is a promising approach to prostate cancer prevention studies. Our earlier studies indicated that the COX-2 inhibitor celecoxib induces apoptosis by also affecting non-COX-2 targets in prostate cancer; substantial evidence from COX-2 knockdown cells will further confirm this finding. Our main focus in this proposed study is to identify the non-COX-2 targets of celecoxib in COX-2 knockdown cell culture models. Recent advances in the application of short interfering RNA (siRNA) followed by microarray analysis, have revolutionized gene function assays both in vitro and in vivo on the basis of knocking down or completely silencing the expression of specific genes. This approach is expected to reveal yet another mode of action for celecoxib. Thus, we propose to create COX-2 knockdown prostate cancer cells with chemically synthesized siRNA, followed by gene expression analysis. We will test the hypothesis that celecoxib activates COX-2 independent molecular targets in prostate cancer. Our specific aims are: (1) to knockdown or silence the expression of COX-2 in prostate cancer cells using siRNA, and (2) to determine the chemopreventive efficacy of low doses of celecoxib in siRNA-mediated COX-2 knockdown prostate cancer cells and its effect on the regulation of non-COX-2 target genes via DNA microarray analysis and RT-PCR. Any possible chemopreventive effect of celecoxib mediated via other anti-inflammatory and apoptosis-inducing genes will be confirmed by RT-PCR and Western blot analysis. A series of logically arranged comprehensive studies will be conducted to validate the gene knockdown effects. Validation of the functions of non-COX-2 targets of celecoxib holds great promise for human prostate cancer prevention trials with potential chemopreventive agents, such as celecoxib.